JP3585276B2 - Method of manufacturing optical thin film and substrate having this optical thin film - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for manufacturing an optical thin film on a substrate at high speed by using a sputtering method and a substrate having the optical thin film.
[0002]
[Prior art]
In the case of forming an optical thin film such as an anti-reflection film, a half mirror, and an edge filter, a vacuum deposition method has been often used in view of easiness of a method and a high film forming speed. On the other hand, in recent years, there has been an increasing demand for coating by a sputtering method which is advantageous in terms of automation, labor saving, and applicability to a large-area substrate as compared with a vacuum evaporation method. However, the spread of the sputtering method is slower than that of the vacuum evaporation method, and thus the spread of the sputtering method has been slightly delayed in industrial use. In particular, when a film of MgF ₂ , which is a typical example of a low refractive index film, is formed by a sputtering method, light absorption is likely to occur. Therefore, formation of an optical thin film by sputtering has been difficult.
[0003]
As a conventional example in which a sputtering method is applied to an optical thin film, there is a method disclosed in JP-A-4-223401. This method targets a material obtained by adding Si to MgF ₂ , which tends to absorb light when sputtering, thereby forming a low-refractive-index film with little light absorption and high durability. I have.
[0004]
[Problems to be solved by the invention]
However, in the above-described conventional example, even when a high frequency power of 2.8 W / cm ² is applied, the film forming rate is 10 nm / min or less at the maximum, and the disadvantage of the sputtering method that the film forming rate is slow can still be solved. Not.
[0005]
The present invention has been made in view of such problems, and provides a method capable of forming a highly durable optical thin film on a substrate at high speed by a sputtering method and a substrate having the optical thin film. It is an object.
[0006]
[Means for Solving the Problems]
In the method for producing an optical thin film of the present invention, a target is MgF ₂ having a particle size of 0.1 to 10 mm, and high-frequency power of ² W / cm ² or more is supplied to the target while introducing a gas containing at least oxygen. Generating a plasma on the target to raise the temperature of the target surface, and forming a MgF ₂ film on the substrate by sputtering both the target and vapor from the target ;
On the film formed in this step, the MgF ₂ as a target, at least while the oxygen introducing a gas containing, physical film thickness 200 nm / min in the following deposition rate, following oxyfluoride optical film thickness is 60nm Forming a magnesium oxide film or a magnesium oxide film .
Further, the substrate having the optical thin film of the present invention targets granular MgF ₂ having a particle size of 0.1 to 10 mm, and applies high frequency power of ² W / cm ² or more to the target while introducing a gas containing at least oxygen. Then, the temperature of the target surface is raised by generating plasma on the target, and the MgF ₂ film on which both the target and the vapor from the target are sputtered, and the refractive index of 1. formed as a hardened layer on this film. A magnesium oxyfluoride film or a magnesium oxide film having an optical film thickness of not less than 40 and an optical film thickness of not more than 60 nm is provided on a substrate as an optical thin film.
[0007]
[Action]
In the conventional sputtering method, when ions collide with the target, it is necessary to break the bonds between the atoms and molecules in the target and cause the atoms and molecules to fly out of the target. Spends breaking the bond. For this reason, the sputtering yield was low, and as a result, there was a drawback that the film formation rate was low. On the other hand, in the present invention, instead of sputtering the solid film raw material as it is, a granular MgF ₂ having a particle size of 0.1 to 10 mm is heated to 700 ° C. or more by plasma generated by high frequency power of ² W / cm ² or more. Heating is performed to increase the vapor pressure sufficiently, and at the same time, the ions are made to collide with the vapor present on the upper portion of the granular raw material so that the energy of the accelerated ions is entirely used for sputtering. For this reason, the sputtering yield is increased, and as a result, the deposition rate can be significantly increased as compared with the conventional method. At this time, not only the vapor but also the granular raw material is sputtered at the same time, but there is no problem from the viewpoint of the film forming speed. Here, limiting the input power to 2 W / cm ² or more has a strict correlation between the input power and the temperature at which the raw material is heated, and when the granular raw material is MgF ₂ , the vapor pressure is sufficiently high. This is because experiments have shown that a heating power of ² W / cm ² or more is required for heating to 700 ° C. or higher. If the size of the granules is too small, they will soar in the chamber and become particles, so the particle size should be 0.1 mm or more. Since the size is reduced, the particle size is preferably 10 mm or less.
[0008]
In addition, it is necessary to reduce light absorption to a level at which there is no practical problem because it is used as an optical thin film. Therefore, it is preferable to perform sputtering while introducing a gas containing oxygen.
[0009]
However, the thin film formed by such a method has a problem that the film surface is slightly damaged when the film is used under severe conditions. According to the present invention, MgF ₂ as a raw material is oxidized by forming a film relatively slowly on a thin film formed by the above method with a relatively small input power, thereby obtaining a hard and scratch-resistant magnesium oxyfluoride or an oxide. It forms magnesium. At this time, there is a correlation between the hardness of the formed thin film and the film forming speed, and when the film forming speed is 200 nm / min or less, the thin film becomes sufficiently hard and hard to be damaged.
The raw material used in this step is not necessarily required to be in the form of granules, and there is no problem even if it is a commonly used plate.
[0010]
Here, it goes without saying that the thicker the hardened layer formed on the surface of the optical thin film, the higher the effect of enhancing the scratch resistance. However, the refractive index of magnesium oxyfluoride or magnesium oxide is 1.4 or more, and although it is difficult to say that the refractive index is sufficiently low, the properties of the antireflection film and the like are deteriorated. For this reason, the optical film thickness is preferably 60 nm or less, and more preferably 20 nm or less.
The optical thin film manufactured on the substrate in this way has scratch resistance and does not deteriorate the characteristics of the film.
[0011]
Embodiment 1
FIG. 1 shows a film forming apparatus used in this embodiment. A substrate 2 is provided above the vacuum chamber 1 so that it can rotate. MgF ₂ granules 3 having a particle size of 3 to 5 mm, which are film materials, are placed in a quartz dish 4 and placed on a magnetron cathode 5 having a diameter of 4 inches (about 100 mm). The cathode 5 is connected to a radio frequency (RF) power source 6 for sputtering. Gas inlets 7 and 9 are provided on the side surface of the vacuum chamber 1.
[0012]
When an optical thin film is formed on a substrate 2 made of BK-based optical glass using this apparatus, first, the inside of the vacuum chamber 1 is evacuated to a degree of vacuum of 1 × 10 ⁻⁴ Pa without heating the substrate 2. . Thereafter, O ₂ gas is introduced from the gas inlet 9 until the degree of vacuum reaches 1 × 10 ⁻¹ Pa. Then, a power of 600 W (that is, 7.6 W / cm ² ) is supplied from the RF power supply 6 to the magnetron cathode 5 to generate plasma. The MgF ₂ granules 3 are heated and sputtered by this plasma. Here, by rotating the substrate 2 and opening the shutter 8, an MgF ₂ film is formed on the substrate 2. The refractive index of the thin film formed under these film forming conditions is 1.38, and the film forming speed is 760 nm / min (physical film thickness). Therefore, the shutter was closed after 6 seconds so that an MgF ₂ film having an optical film thickness of 105 nm was formed on the substrate 2.
[0013]
Subsequently, 300 W (that is, 3.8 W / cm ² ) of electric power was supplied from the RF power supply 6 to the magnetron cathode 5 to perform sputtering. The refractive index of the thin film formed under these film forming conditions is 1.45, and the film forming speed is 200 nm / min (physical film thickness). For this reason, the shutter was closed after 4 seconds so that a thin film having an optical film thickness of 20 nm was formed on the substrate.
[0014]
FIG. 2 shows the spectral reflectance of the antireflection film formed as described above. Sufficient characteristics of about 2% or less were obtained in the entire visible region (wavelength 400 to 700 nm). Next, a scratch resistance test was performed by rubbing 500 times with steel wool, and there was no visible scratch on the film surface.
As described above, according to this embodiment, a highly durable anti-reflection film can be formed in only 10 seconds without heating the substrate.
[0015]
FIG. 3 shows the spectral reflection characteristics of the present embodiment when no hardened layer is provided on the surface. The reflection characteristic is slightly lower than that of this embodiment, and shows slightly superior characteristics. However, when a similar abrasion resistance test was performed using steel wool, scratches that could be visually confirmed after rubbing about 20 times were found.
[0016]
Embodiment 2
Using the same apparatus as in Example 1, an optical thin film was formed. A plastic plate was used as the substrate 2 and was not heated. O2 gas was introduced from the gas inlet 7 to a vacuum of 5 × 10 ^-1 Pa, and then Ar gas was introduced from the gas inlet 9 to a vacuum of 5 × 10 ^-2 Pa. Sputtering was performed at an input power of 160 W (that is, 2 W / cm ² ), and a film having a refractive index n of 1.38 and an optical film thickness nd of 70 nm was formed on the substrate 2 in 14 seconds. In this case, from the refractive index n = 1.38, the optical film thickness nd = 70 nm, and the film forming time of 14 seconds, the film forming speed is 217 nm / min (physical film thickness). Subsequently, sputtering was performed at an input power of 100 W, and a film having a refractive index of n = 1.40 and an optical thickness of nd = 60 nm was formed on the substrate 2 in 30 seconds. The film formation rate at this time was 86 nm / min (physical film thickness).
[0017]
The film formed in this embodiment has sufficient adhesion and scratch resistance, and can be used as an antireflection film for sunglasses, goggles, displays, and the like.
[0018]
Embodiment 3
In this embodiment, an optical thin film is formed by using the same film configuration and the same apparatus as in the first embodiment. In this embodiment, a film was formed by introducing CO2 gas from the gas inlet 9 until the pressure reached 1 × 10 ^-1 Pa. When a power of 600 W was applied from the RF power supply 6 in this step, the film formation rate was 950 nm / min (physical film thickness), which was higher than that of Example 1 and could be formed in 5 seconds. In the next step, a plate-like target was used in place of the granules, CO2 gas was introduced from the gas inlet 9 until the pressure reached 8 × 10 ^-1 Pa , and power of 600 W was supplied from the RF power supply 6. The film formation rate in this step was 50 nm / min (physical film thickness), and the film formation was completed in 16 seconds. The abrasion resistance of the formed film was sufficient as in Example 1.
[0019]
In the above embodiment, the example of use of the antireflection film is shown. However, it is needless to say that the present invention may be used for another optical thin film, for example, a half mirror or an edge filter.
[0020]
【The invention's effect】
As described above, according to the present invention, instead of sputtering a solid film material as it is, granular MgF ₂ having a particle size of 0.1 to 10 mm is generated by high-frequency power of ² W / cm ² or more. The plasma is heated by the plasma to increase the vapor pressure sufficiently, and the ions are made to collide with the vapor present above the granular raw material so that all the energy of the accelerated ions is used for sputtering. For this reason, the sputtering yield is increased, and as a result, the deposition rate can be significantly increased as compared with the conventional method. Further, by forming a film on this film relatively slowly, the raw material MgF ₂ is oxidized to form hard and scratch-resistant magnesium oxyfluoride or magnesium oxide. It is possible to form a thin film having high properties, especially scratch resistance.
Therefore, in the substrate having the optical thin film manufactured as described above, the optical thin film has high durability and can be formed at a high speed, so that it can be easily spread industrially.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a film forming apparatus used in an example.
FIG. 2 is a spectral reflection characteristic diagram of the antireflection film of Example 1.
FIG. 3 is a spectral reflection characteristic diagram of an antireflection film having no cured layer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Vacuum tank 2 Substrate 3 Granule 4 Dish 5 Magnetron cathode 6 RF power supply 7 Gas inlet 9 Gas inlet

Claims (5)

By targeting a granular MgF ₂ having a particle size of 0.1 to 10 mm and introducing a gas containing at least oxygen, a high frequency power of ² W / cm ² or more is supplied to the target to generate plasma on the target. Forming a MgF ₂ film on the substrate by raising the temperature of the target surface and sputtering both the target and vapor from the target;
On the film formed in this step, while using a gas containing at least oxygen with a target of MgF ₂ at a film formation rate of a physical film thickness of 200 nm / min or less and an optical film thickness of 60 nm or less on the film formed in this step. Forming a magnesium oxide film or a magnesium oxide film. By targeting a granular MgF ₂ having a particle size of 0.1 to 10 mm and introducing a gas containing at least oxygen, a high frequency power of ² W / cm ² or more is supplied to the target to generate plasma on the target. An MgF ₂ film in which the temperature of the target surface is increased and both the target and the vapor from the target are sputtered;
A magnesium oxyfluoride film or a magnesium oxide film having a refractive index of 1.40 or more and an optical film thickness of 60 nm or less formed as a cured layer on the film;
A substrate having an optical thin film, comprising: The granular MgF ₂ 2. The method for producing an optical thin film according to claim 1, wherein the target is heated to 700 ° C. or higher by plasma generated on the target. The method according to claim 1, wherein the substrate is not heated during film formation. The oxygen-containing gas introduced during the film formation is O 2 ₂ Gas, CO ₂ 2. The method according to claim 1, wherein the gas is a gas.

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